They've argued both interfere with existing uses of the fairgrounds that are protected by either Metro or state law.

Petitioners held a news conference outside the Metro courthouse Wednesday to announce the suit's filing in Davidson County Chancery Court. It comes as a city groundbreaking for the fairgrounds park had been scheduled for Thursday and three weeks after the Metro Council voted 31-6 to approve bond funding for the stadium proposed by Mayor Megan Barry.

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"The real purpose of this lawsuit is to hopefully stop the Metropolitan government from destroying the fairgrounds," said attorney Jim Roberts. "Everything that the fair board has done the last few months to try to bring MLS soccer is going to destroy its ability to conduct a state fair."

Roberts, on behalf of a similar coalition including Save Our Fairgrounds, earlier this month filed a separate lawsuit against Metro over Barry's redevelopment proposal called Cloud Hill slated for the city's old Greer Stadium site.

In the latest lawsuit, petitioners have argued the new stadium, 10 acres of fairgrounds land set aside for private development as part of the stadium plan, and the fairgrounds park would each "negatively affect and violate" protected uses outlined in a fairgrounds referendum Nashville voters approved in 2011. The charter amendment approved in 2011 says that all existing fairgrounds activities, including auto-racing, expo center events and flea market events, are to continue on the site.

In addition, the lawsuit says the five-member Metro fair board is obligated to conduct annual state fair by state law.

Plaintiffs have argued that the elimination of more than 45 acres of dedicated parking, which also produces revenue for the fairgrounds, would interfere with traditional uses, including the state fair.

In a statement, mayor's office Press Secretary Sean Braisted said the administration had not seen the lawsuit nor do they comment on pending litigation. He said they are confident the soccer stadium proposal complies with all laws and charter provisions.

"It was debated very publicly for more than a month with ample opportunities for public comment and input," he said. "The overwhelming majority of the Metro Council and the public support this project. We look forward to the MLS announcement in December as to whether Nashville will be chosen to receive an MLS franchise. If so, there will be more detailed discussions and planning with community input to ensure that construction of the stadium at the Fairgrounds positively impacts the community and existing users."

Fair board chairman Ned Horton said the park groundbreaking that was set for Thursday has been rescheduled to a still-to-be-determined date. He cited a scheduling conflict unrelated to the lawsuit.

Barry has vowed to continue all existing activities at the fairgrounds even with the MLS stadium, which would only get built if Nashville is awarded a team. The plan calls for rebuilding expo facilities that would need torn down for the stadium and to work around the flea market schedule.

Fairgrounds Director Laura Schloesser has offered support for the revamped fairgrounds and said her staff can make existing fairgrounds activities and MLS soccer co-exist. Meanwhile, the state commission that operates the annual Tennessee State Fair started exploring sites outside of Nashville months before the council approved the stadium.

Clint Brewer, a spokesman for Nashville's MLS ownership group led by businessman John Ingram, said the ownership group and MLS2Nashville are not parties to the filing and can't comment on the lawsuit.

Reach Joey Garrison at 615-259-8236, jgarrison@tennessan.com and on Twitter @Joeygarrison.